Christie, Samuel Hunter
Christie, Samuel Hunter
(b. London, England, 22 March 1784; d. Twickenham, London, 24 January 1865),
magnetism.
Christie was the only son of James Christie, founder of the well-known auction galleries, and his second wife, formerly Mrs. Urquhart. Samuel was educated at Walworth School, Surrey, and Trinity College, Cambridge, which he entered as a sizar in October 1800. He was active in athletics and was a brother officer with Lord Palmerston in the grenadier company of University Volunteers. In 1805 he took his bachelor’s degree as second wrangler and shared the Smith’s prize with Thomas Turton. Appointed third mathematical assistant in Woolwich Military Academy in July 1806, Christie became professor of mathematics there in June 1838. He made major revisions in the curriculum, raising it to a high standard.
Christie was elected a fellow of the Royal Society on 12 January 1826, frequently served on the Society’s council, and was its secretary from 1837 to 1854. He married twice and by his second wife, Margaret Malcom, was the father of the future Sir William H. M. Christie, astronomer royal from 1881 to 1922. Samuel H. Christie was a vice-president of the Royal Astronomical Society and one of the visitors of the Royal Observatory, Greenwich. Owing to ill health, he retired from his professorship in 1854 and moved to Lausanne.
Almost all of Christie’s investigations were related to terrestrial magnetism. In June 1821, while studying the influence of an unmagnetized iron plate on a compass, he discovered “that the simple rotation of the iron had a considerable influence on its magnetic properties.”1 Although he delayed making a detailed announcement of his results until June 1825, Christie did refer to this discovery in June 1824.2 His work was independent of, and prior to, Arago’s report of the magnetic influence of rotating metals. From his experiments he concluded that since “the direction of magnetic polarity, which iron acquires by rotation about an axis… has always reference to the direction of the terrestrial magnetic forces,… this magnetism is communicated from the earth.”3 He then went on to speculate that the earth in turn receives its magnetism from the sun.
In other papers Christie reported on a method for separating the effects of temperature from observations of the diurnal variation of the earth’s magnetic field. In addition he speculated that this variation is caused by thermoelectric currents in the earth produced by the sun’s heating.4 Christie also observed a direct influence of the aurora on the dip and horizontal intensity of the earth’s magnetic field.5 As a recognized authority, Christie prepared a “Report on the State of Our Knowledge Respecting the Magnetism of the Earth” for the 1833 meeting of the British Association, reported on the magnetic observations made by naval officers during various polar voyages, and was the senior reporter on Alexander von Humboldt’s proposal that cooperating magnetic observatories be founded in British possessions.6
Christie’s paper “Experimental Determination of the Laws of Magneto-electric Induction…” was the Bakerian lecture for 1833. In it Christie showed that “the conducting power, varies as the squares of [the wires’] diameters directly, and as their lengths inversely.” He also concluded that voltaelectricity, thermoelectricity, and magnetoelectricity are all conducted according to the same law, which lent further support to the theory that all these electricities are identical.7 In this paper Christie also gave the first description of the instrument that came to be known as the Wheatstone bridge.
NOTES
1.Edinburgh Journal of Science, 5 (July 1826), 12–13.
2.Philosophical Transactions of the Royal Society, 115 (1825), 347–415; ibid., 58n.
3.ibid., 411.
4.Philosophical Transactions, 113 (1823), 342–392; ibid., 115 (1825), 1–65; ibid., 117 (1827), 308–354.
5.Journal of the Royal Institution of Great Britain, 2 (Nov. 1831), 271–280.
6.Report of the British Association for the Advancement of Science (1833), pp. 105–130; Philosophical Transactions, 116 (1826), pt. 4, 200–207; ibid., 126 (1836), 377–416; Proceedings of the Royal Society, 3 (1837), 418–428.
7.Philosophical Transactions, 123 (1833), 130, 132.
BIBLIOGRAPHY
I. Original Works. These are listed in the Royal Society’s Catalogue of Scientific Papers. He also published An Elementary Course of Mathematics for the Use of the Royal Military Academy and for Students in General, 2 vols. (London,1845–1847). The library of the Royal Society has some of his manuscript letters and reports.
The following are Christie’s most important papers, and information in this article is based upon them: “On the Laws According to Which Masses of Iron Influence Magnetic Needles,” in Transactions of the Cambridge Philosophical Society, 1 (1822), 147–173; “On the Diurnal Deviations of the Horizontal Needle When Under the Influence of Magnets,” in Philosophical Transactions of the Royal Society, 113 (1823), 342–392; “On the Effects of Temperature on the Intensity of Magnetic Forces; and on the Diurnal Variation of the Terrestrial Magnetic Intensity,” ibid., 115 (1825), 1–65; “On the Magnetism of Iron Arising From Its Rotation,” ibid., 347–417; “On Magnetic Influence in the Solar Rays,” ibid., 116 (1826), 219–239; “Experimental Determination of the Laws of Magneto-electric Induction in Different Masses of the Same Metal, and of Its Intensity in Different Metals,” ibid., 123 (1833), 95–142; “Report on the State of Our Knowledge Respecting the Magnetism of the Earth,” in Report of the British Association for the Advancement of Science (1833), 105–130; with G. B. Airy, “Report Upon a Letter Addressed By M. le Baron de Humboldt to His Royal Highness the PRS, and Communicated by HRH to the Council,” in Proceedings of the Royal Society, 3 (1837), 418–428.
II. Secondary Literature. Very little secondary literature exists on the history of magnetism, and Christie is infrequently mentioned in that. Biographical information can be found in the Dictionary of National Biography and in the sources listed there, as well as in William Roberts, Memorials of Christie’s, 2 vols. (London, 1897), and H. D. Buchan-Dunlop, ed., Records of the Royal Military Academy, 1741–1892 (Woolwich, 1895). The most useful, although very old, account of the history of magnetism up to about 1831 id [Sir David Brewster] “Magnetism,” in Encyclopaedia Britannica, 7th and 8th eds.
Edgar W. Morse